Glow discharge circuits



p 1958 F. HARDERS ETAL 2,853,655

GLOW DISCHARGE CIRCUITS Filed June 14, 1955 United States P fl O2,853,655 GLOW DISCHARGE CIRCUITS Fritz Harders, Post Ergste uberS'chwerte-Ruhr, Helmut Kniippel, Dortmund-Lottringhausen, and KarlBrotzmann, Dortmund, Germany,'assignors to Dortmund- Hiirder HuttenunionAktiengesellschaft, Dortmund, Germany Application June 14, 1Sl55, SerialNo. 515,426 Claims priority, application Germany June 16,1954 6 Claims.(Cl. 315-241 use of a low ohmic limiting resistance leads, when thedischarge changes over to an arc discharge, to a momentary very largecurrent which not only endangers the electric installation but makes anundesired burn mark on the object to'be treated.

Bymeans of the invention it is possible to overcome the above-mentioneddisadvantages and to maintainj a suitable glow discharge of high currentstrength; i."e.', a current intensity exceeding 1 amp and in mostinstances 10 amps, in continuous operation with a relative lowconsumption'of energy. This result is obtained inthat, by means ofsuitable electric circuit elements, the negative current-voltagecharacteristic of the arc is used, when the glow discharge changes over,to extinguish the are im mediately. As the circuit element there isused, in accordance with the invention, a condenser which is connectedin parallel with the glow discharge path and of which the capacity,taking into account the limiting resistance connected in series with thedischarge path, is so selected that, when the glow discharge changesover into an arc discharge, the latter causes the arc discharge to bequickly extinguished by utilising the dropping characteristic of the arcdischarge. There may also be provided for the gas discharge vessel anignition device of a known kind which is so dimensioned and designedthat the gas discharge is initiated approximately when the necessaryglow discharge voltage is reached, and is therefore, automatically setin operation. The current strength and the gas pressure in the dischargevessel are so adjusted that the glow discharge is operated as far aspossible in the range of the anormal cathode drop.

Further details of the invention are illustrated, by way of example, inthe drawing which shows the electric circuit.

In the drawing the discharge vessel is designated by the reference G,the parallel condenser by the reference C, the series limitingresistance by the reference R and the source of current, which ispreferably adjustable, by the reference S. The limiting resistance R isso dimensioned that normally a. glow discharge is maintained in thedischarge vessel G. If now the glow discharge changes over into an arcdischarge, then the condenser C is discharged to the voltage drop at thedischarge path. Consequently, there flows through the limitingresistance R for a very short time a considerably stronger current thancan be delivered by the source of current S alone. This causes a furtherheavy drop in the operating voltage. However,

2,853,655 Patented Sept. 23, 1958 ice . 2 the current which is nowsupplied only through the limiting voltage R is no longer sufiicient forthe low operating voltage, so that the discharge is extinguished. Thiseffect is still further promoted by the condenser C which is onlycharged again when the voltage increases.

It has been found by experiment that the duration for which the arcburns is, in general, so'short that no burn mark is produced onthecathode on the discharge vessel. Further the occurrence of a burn markcan be avoided with certainty by connecting, in the circuit whichcontains the gas discharge path and is in parallel with the condenser C,a resistance-R which is considerably smaller than the limitingresistance R which resistance R receives the energy of the condensercorresponding to the high current strength.

In order to produce a stable glow discharge of 50 amperes, theindividual circuit elements may be dimensioned for example as follows:

R =7 ohms, R2=0.02 ohms, c=40 f.

In order to maintain the loss ofenergy which occurs when operating glowdischarge as small as possible, itis advantageous to keep the limitingresistance connected in series with the discharge path as small aspossible. In the above-mentionedcircuit, however, the size ofthelimiting resistance has a lower limit owing to its cooperation with thecondenser. 7

According to further features of the invention the above-mentionedlimitation isjavoided, in that there is connected in series with thelimiting resistance an additional choke L which, when the glow dischargechanges to an arc discharge, limits themomenta'ry current which flows toa considerably greater extent than an ohmicresistance. It is thenadvantageousto dimension the choke L, the limiting resistancei Rahd-thecondenser C'in such a way that'a damped' 'oscillating circuit isformed, the first voltage 'maxiniumof-which is so high that the glowdischarge is again initiated without external ignition.

The limitation of the current flowing when the glow discharge changesover to an arc discharge when the choke L is present is no longeretfected solely by the limiting resistance R but to a considerablystronger extent at the moment of change-over owing to the inductance L.The ignition device Z, for again initiating the glow discharge afterbeing extinguished can be omitted,

if as above-mentioned, R, L and C are properly dimensioned. Theresistance R illustrated in the drawing is considerably smaller than theresistance R and for this purpose the ohmic resistance of the leads isgenerally sufiicient. The resistance R serves the purpose of takingconsiderable part of the energy of the condenser C when the glowdischarge changes over to an arc discharge.

For the continuous operation of a glow discharge of 200 amperes thecircuit elements may, for example, be dimensioned as follows:

R =1 ohm; C= t; L=5 microhenries and R =0.0002 ohms The operation of thecircuit according to the invention will now be explained in more detail.

Experimental recordings indicate that the breakdown of the glowdischarge to an arc discharge initiates an oscillation of approximatelysinusoidal character, causing the voltage across the capacitor C todecrease to negative values. Extinction of the arc occurs almostsimultaneously with the negative peak of the voltage across thecapacitor C. This is readily understood since at this particular instantthe current in the vessel would have to change sign. With the currentpath through the vessel interrupted, the circuit reduces to a simpleRC-network. The capacitor voltage now increases exponentially until apositive voltage value across the vessel is reached which issufiiciently high to reinstate the glow discharge. As a'matter ofinterest, the time between breakdown and extinction was found to amountto something between 10% and 10 seconds. This is by far less than an arcdischarge requires to build up ,cornpletelyiand to do any harm,Visually, the. breakdown appears in the form of an extremely short andrather dim flash. No real arc is observed. i

Considering'that an electric oscillation requires the presence ofinductance as well as capacitance, there is good reason to believe thatthe inductance inherent in the mesh comprising vessel G, capacitor C andthe leads connecting the two takes an active'part in the process.

Quantitative analysis shows that the efiective inductance amounts tojusta few microhenries, an amount'always present in'a circuit of thephysical size involved here.

Hence it isunnecessary to provide an inductance in the mesh referred toby inserting a coil. In fact, this was never done.

We claim:

1. In an apparatus for snrtace-treating metal objects or the like in avacuum vessel in the presence of a con tinuously burning glow discharge,in combination: a glow discharge vessel adapted to operate at currentsexceeding 1 amp.; a pair 'of electrodes 'spac'edly ar'ranged inside saidvessel; a source of electric energy;,,affirst resistor and a secondresistor; said electrodes, said electric energy source and said firstresistor being connected in series; and a capacitor connected inparallel to said electrodes and said second resistor; the resistance ofsaid first resistor being less than the resistance across saidelectrodes and saids econd resistor, when a glow discharge is presentinsaid vessel; whereby an arc discharge resulting from a breakdown of aglow discharge in said glow discharge vessel is extinguished and saidglow discharge reinstated.

2, In an apparatus as claimed in claim 6, a choke connected in serieswith said resistor.

3. In an apparatus as claimed in claim 2, the lower limit of the productof the resistance of said resistor and the capacitance of said capacitorbeing of the order of 10- seconds.

4. In an apparatus as claimed in claim 3, said glow discharge vesselbeing adapted to operate at a current of the order of amps, saidresistor having a resistance of the order of 7 ohms, and said capacitorhaving a capacitance of the order of 40 microfarads.

5. In an apparatus as claimed inclaim 3, said glow discharge vesselbeing adapted to operate at a current of the order of 200 amperes, saidresistor having a resistance of the order of 1 ohm, and said capacitorhaving a capacitance of the order of microfarads.

6. In an apparatus for surface-treating metal objects or the like inavacuum vessel inthe presence of a continuously burning glow discharge,in combination a glow discharge vessel adapted to operate at currentsexceeding 1 ampere; a pair of electrodes spacedly arranged inside saidvessel; a source of electricenergy; a first resistor; a second resistor,said electrodes, said second resistor, said first resistor and saidsource of electricalenergy being connected in series; and a capacitorconnected'in parallel to said electrodes and said second resistor, theresistance of said first resistor being less than the resistance acrosssaid electrodes and the second resistor, whereby an arc dischargeresulting from a breakdown of a glow'discharge in said glow dischargevessel is extinguished and said glow discharge reinstated.

References Cited in the file of this patent UNITED STATES PATENTS2,258,149 Schultze Oct. 7, 1941 2,391,611 Back Dec. 25,1945 2,550,089Schlestnan Apr. 2.4, 1951 2,553,944 Schlesman May 22., 1951 2,728,877Fisher Dec. 27,1955

FOREIGN PATENTS 618,256 Great Britain Feb., l8 1949

